@article{10_4171_dm_24,
     author = {Christian Leis},
     title = {Hopf-bifurcation in systems with spherical symmetry. {I:} {Invariant} tori},
     journal = {Documenta mathematica},
     pages = {61--113},
     year = {1997},
     volume = {2},
     doi = {10.4171/dm/24},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/dm/24/}
}